1. Field of the Invention
The present invention relates generally to a partial-response record signal regenerating method and an apparatus thereof that make use of partial-response signaling with a maximum-likelihood sequence detection and, more particularly, to a partial-response record signal regenerating method and an apparatus thereof that improve a process of detecting a start-of-decode position.
2. Description of the Related Art
In recent years, partial-response signaling with maximum-likelihood sequence detection (PRML) has hitherto been utilized in order to enhance recording densities of a magnetic disc and a magneto-optic disc apparatus. In such a PRML system, when data is written to the magnetic disc, the data is coded. For example, 8-bit data is converted into 9-bit data by use of 8/9 conversion codes, and the data is thus written to the magnetic disc. Conversely when reading the data from the magnetic disc, it becomes necessary to decode the data in accordance with the conversion codes and thus set the data back in the original form.
In the case of this decoding, it is required that the coded data be decoded according to every set of data. For instance, in the case of the 8/9 conversion, the data is decoded into 8 bits according to every 9-bit data. Hence, it is necessary to detect a start-of-position for decoding the data.
In the disc storage apparatus which utilizes the partial-response signaling, a maximum-likelihood sequence detector reconstructs a string of data recorded, and, a receiving filter (equalizing circuit) of the regenerating apparatus is required to shape an output signal of a record channel into a partial-response signal. For this purpose, a training signal is written to a storage disc. Then, this training signal is read, and the equalizing circuit such as an electric filter and a cosine equalizer is trained. That is, the equalizing circuit is adapted to a partial-response characteristic corresponding to a track radius on the disc.
Such a system is disclosed in the specifications of U.S. Pat. Nos. 5,060,088, 4,644,564, 4,707,681, 4,786,890 and 4,888,775.
In such a PRML system, an item of synchronous data known as a sync byte is written into a heading of the data. Then, the start-of-decode position is detected beforehand by detecting this sync byte. For example, in the case of a 8/9 conversion, the data is decoded by 9 bits from the start-of-decode position detected using the sync byte.
According to this technique, however, it is required that the sync byte be written into a data area. For this reason, the data area in which the actual data are recorded is reduced. This leads to a problem that the actual data storage capacity decreases.